The disarticulation of a hip involves a replacement of an entire leg including the hip joint with a prosthesis designed to provide a portable, patient-controlled, stable platform on which the patient can rest his weight during the prosthesis weight bearing phase of the stride. In general, the prosthesis device primarily uses passive components having two major sections; a trunk socket in which the body portion of the replaced leg is received, and an artificial leg section including a thigh section, a lower leg section, and a foot section. Simple hinges join the sections at an artificial hip joint and the knee. Optimum performance is obtained through the proper alignment of the "prosthesis" section. Once the prosthesis is properly aligned and after a small amount of training, a patient can regain the ability to walk, but normally the patient's gait is badly distorted.
The distortion is caused primarily by the maneuvers through which the patient must go to lift the prosthetic leg and swing it forward to take the next step. The normal leg during its normal swing is flexed at both the hip and knee thus providing adequate clearance between the foot and the ground. Unfortunately, this is not the case with the artificial leg which is at its maximum length as the foot passes closest to the ground leaving no clearance since both the natural leg and the artificial leg are the same length. To obtain clearance, the patient elevates his hip on the prosthesis side and swings his prosthesis or artificial leg slightly to the side when bringing it forward or the patient vaults by raising on the toe of the normal foot in order to obtain clearance of the artificial leg. Obviously, the net result is a distorted gait.
The present invention provides a needed actuator device that can be attached to the prosthesis to store energy during one phase of the stride, and release this energy during another phase to pivot the artificial hip joint much as the natural hip joint flexes so as to eliminate a considerable amount of the gait distortion while also providing a faster cadence than might otherwise be possible. The device must be reliable and durable, and must be lightweight. The device must not interfere with the prosthesis assuming an extreme position such as sitting, but must move the thigh section forward rotating the thigh section approximately 20.degree. about the hip pivot axis as the prosthetic foot leaves the ground. The amount of forward motion imparted to the thigh section must be closely controlled as too much motion will prevent the proper prosthesis alignment needed for the next step, and too little motion does not solve the gait distortion problem.